Error: type mismatch: got 'proc ()' for 'handleOOM' but expected 'proc (){.nimcall, gcsafe.}'

[forchid]

Nim Version

Nim Compiler Version 2.2.2 [Windows: amd64]
Compiled at 2025-02-06
Copyright (c) 2006-2025 by Andreas Rumpf

active boot switches: -d:release

Description

According to the nim 2.2.2 stdlib system website example, it can't be compiled. If adding the pragmas {.nimcall, gcsafe.} then re-compiling it, the Error: 'handleOOM' is not GC-safe as it accesses 'gOutOfMem' which is a global using GC'ed memory was thrown.

var gOutOfMem: ref OutOfMemDefect #EOutOfMemory
new(gOutOfMem) # need to be allocated *before* OOM really happened!
gOutOfMem.msg = "out of memory"

proc handleOOM() =
  raise gOutOfMem

system.outOfMemHook = handleOOM

Current Output

>nim c -d:release oomhook
Hint: used config file '..\.choosenim\toolchains\nim-2.2.2\config\nim.cfg' [Conf]
Hint: used config file '..\.choosenim\toolchains\nim-2.2.2\config\config.nims' [Conf]
.......................................................................
..\oomhook.nim(8, 23) Error: type mismatch: got 'proc ()' for 'handleOOM' but expected 'proc (){.nimcall, gcsafe.}'
  Pragma mismatch: got '{..}', but expected '{.gcsafe.}'.

Expected Output

Compiling passes.

Known Workarounds

No response

Additional Information

No response

[Araq]

Try this:

proc handleOOM() {.nimcall, gcsafe.} =
  {.cast(gcsafe).}:
    raise gOutOfMem

But also, the runtime wasn't hardened against handling OOM gracefully. Unfortunately. PRs are welcome. At least the new Nimony compiler's core library was designed with this in mind.

[forchid]

{.cast(gcsafe).}

@Araq Compiling passed, but the system.outOfMemHook is invalid in following test program.

# maxmem.nim
var oom = false;
var a = newSeq[seq[byte]]();

proc main() =
    for i in 0 .. 100000:
        let b = newSeq[byte](1 shl 20)
        a.add(b)
        if i mod 1000 == 0:
            echo("i = " & $i)
    
    echo "ok."

var outom: ref OutOfMemDefect
new(outom)
outom.msg = "Fatal: out of memory!"

system.outOfMemHook = proc () =
    oom = true
    {.cast(gcSafe).}: raise outom
    
try:
    main()
except Exception as e:
    echo "Fatal: " & e.msg
finally:
    echo "Bye!"
discard readLine(stdin)

The test result

>maxmem
i = 0
i = 1000
i = 2000
i = 3000
i = 4000
i = 5000
i = 6000
i = 7000
i = 8000
i = 9000
i = 10000
i = 11000
i = 12000
i = 13000
i = 14000
i = 15000
out of memory

[Araq]

So fix it.